[Android] Add a native pull-to-refresh overscroll effect

content/browser/android/content_view_core_impl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_ANDROID_CONTENT_VIEW_CORE_IMPL_H_
 #define CONTENT_BROWSER_ANDROID_CONTENT_VIEW_CORE_IMPL_H_
 
 #include <vector>
 
 #include "base/android/jni_android.h"
@@ skipping 33 matching lines @@
                       WebContents* web_contents,
                       ui::ViewAndroid* view_android,
                       ui::WindowAndroid* window_android,
                       jobject java_bridge_retained_object_set);
 
   // ContentViewCore implementation.
   virtual base::android::ScopedJavaLocalRef<jobject> GetJavaObject() override;
   virtual WebContents* GetWebContents() const override;
   virtual ui::ViewAndroid* GetViewAndroid() const override;
   virtual ui::WindowAndroid* GetWindowAndroid() const override;
-  virtual scoped_refptr<cc::Layer> GetLayer() const override;
+  virtual const scoped_refptr<cc::Layer>& GetLayer() const override;
   virtual void ShowPastePopup(int x, int y) override;
   virtual void GetScaledContentBitmap(
       float scale,
       SkColorType color_type,
       gfx::Rect src_subrect,
       const base::Callback<void(bool, const SkBitmap&)>& result_callback)
       override;
   virtual float GetDpiScale() const override;
   virtual void PauseOrResumeGeolocation(bool should_pause) override;
   virtual void RequestTextSurroundingSelection(
@@ skipping 224 matching lines @@
   virtual void RenderViewHostChanged(RenderViewHost* old_host,
                                      RenderViewHost* new_host) override;
   virtual void WebContentsDestroyed() override;
 
   // --------------------------------------------------------------------------
   // Other private methods and data
   // --------------------------------------------------------------------------
 
   void InitWebContents();
 
-  RenderWidgetHostViewAndroid* GetRenderWidgetHostViewAndroid();
+  RenderWidgetHostViewAndroid* GetRenderWidgetHostViewAndroid() const;
 
   blink::WebGestureEvent MakeGestureEvent(
       blink::WebInputEvent::Type type, int64 time_ms, float x, float y) const;
 
   gfx::Size GetViewportSizePix() const;
   int GetTopControlsLayoutHeightPix() const;
 
   void SendGestureEvent(const blink::WebGestureEvent& event);
 
   // Update focus state of the RenderWidgetHostView.
@@ skipping 35 matching lines @@
       java_bridge_dispatcher_host_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentViewCoreImpl);
 };
 
 bool RegisterContentViewCore(JNIEnv* env);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ANDROID_CONTENT_VIEW_CORE_IMPL_H_